Shark Movements Can Be Used to Design Better Marine Protected Areas

Source Article: Klimley, A.P., Arauz, R., Bessudo, S. et al. Studies of the movement ecology of sharks justify the existence and expansion of marine protected areas in the Eastern Pacific Ocean. Environ Biol Fish (2022).

Featured Image Caption: A Galapagos shark (Carcharhinus galapagensis), one of the sharks in the Eastern Tropical Pacific that was tracked. Image Source: Wikipedia Creative Commons by Tam Warner Minton

Tam Warner Minton from DAllas, usa, CC BY 2.0, via Wikimedia Commons

Commercial fishing has been endangering sharks for decades. Shark populations worldwide decreased between 1970 and 1995, sparking fears of extinctions. While this decline has slowed recently, many successes of shark conservation are limited to specific regions. The good news is that by improving our management practices, we have seen that we can help increase and stabilize their numbers. To do this, scientists are studying the best ways to manage shark populations.

Marine protected areas (MPAs) are one highly effective strategy for conserving sharks and other marine life. In some marine protected areas, known as “no-take” areas, fishing and other activities, like mining ores from the ocean floor, are illegal. There are many areas around the world with this designation, and they provide animals like sharks with safe places to grow and reproduce. However, for these protected areas to be effective, they must include the locations where wildlife already spend time. In the ocean, animals are not spread evenly, but often congregate around seamounts and islands. Therefore, to protect oceanic life most effectively, MPAs should include these hotspots of wildlife. In recent decades, researchers have used the actual locations of sharks over time to create the borders of several MPAs. Researchers have also found that this highly successful strategy has additional untapped potential for shark conservation.

Tracking Sharks and Fishers

Defining borders of MPAs based on the locations of animals and ensuring the protection of large swaths of ocean require that scientists monitor how the wildlife and fishers in the protected area are behaving. Telemetry, the recording and automatic transmission of data from remote places, is a vital tool for this sort of large-scale monitoring problem. Researchers have tracked sharks with two types of telemetry: coded ultrasonic beacons and satellite transmitters.

Scalloped hammerhead shark (Sphyrna lewini), one of the sharks tagged by researchers for this study. These sharks spent much of the year around particular islands. Image Source: Wikipedia Creative Commons by Barry Peters
Barry Peters`, CC BY 2.0, via Wikimedia Commons

Coded ultrasonic beacons are small electronic tags placed on sharks either internally or externally that send a particular pitch of ultrasonic sound wave (outside the range of human hearing) to receivers placed on island coasts. To place a tag internally, researchers catch the shark by hook and line, make a small cut, insert the tag, and then close the wound with stitches. To place a tag externally, researchers shoot a dart into the upper side of the shark with the tag attached on a tether. These methods allow scientists to identify sharks close to islands of interest over the course of years.

Satellite transmitters are electronic tags placed externally on sharks that send a radio signal to satellites in orbit. These transmitters allow scientists to locate and identify sharks very precisely whether sharks are close to land or in the open ocean.

In addition to tracking sharks, researchers have used beacons on fishing boats and satellite imagery to see how effective the MPAs are at reducing fishing. These beacons, which are mandatory for commercial fishing boats, send signals to satellites to communicate their location and identity. Satellite images can locate boats fishing illegally without beacons.

So, are MPAs protecting sharks?

By using these telemetric techniques as long ago as 2002, four MPAs in the Eastern Tropical Pacific, off the coast of Central America, were able to draw or expand their borders based on sharks’ preferred habitats. Telemetric data revealed that some species of sharks spent large fractions of the year near particular islands and moved around between neighboring islands frequently. Specifically, silvertip, scalloped hammerhead, tiger, dusky, Galapagos, silky, blacktip, and whitetip reef sharks stayed local to certain groups of islands monitored in the study for weeks or months. This finding demonstrated the importance of protecting large areas around whole groups of islands, or archipelagos.

Four MPAs in the Eastern Tropical Pacific that have utilized shark tracking to guide the creation or expansion of their borders: Revillagigedo National Park, Mexico; Cocos Island National Park, Costa Rica; Malpelo Fauna and Flora Sanctuary, Colombia; Galapagos Marine Reserve, Ecuador. Map source: edited pat Public Domain World Maps

Recently, researchers have used telemetric data to see how effective two of these MPAs have been at reducing fishing, and whether the current boundaries still make sense based on the latest data. The formation of the two no-take areas almost entirely stopped the fishing at each MPA, meaning that they were highly effective in protecting wildlife. Specifically, the Malpelo Fauna and Flora Sanctuary and the National District of the Yuparí-Malpelo National Integrated Management District (DNMI) off the coast of Colombia had almost no fishing activity within the protected areas. Similarly, the creation of Revillagigedo National Park off the coast of Mexico, the largest no-take area near the American Continent, effectively ended fishing within the park, and even made commercial fishing directly outside the MPA more productive!

One of the Revillagigedo Islands, off the coast of Mexico (left), and Cocos Island, off the coast of Costa Rica (right). Image Sources: Wikipedia Creative Commons by Presidencia de la República Mexicana and by Jon Rawlinson
Presidencia de la República Mexicana, CC BY 2.0, via Wikimedia Commons
Jon Rawlinson, Creative Commons Attribution 2.0 Generic, via Wikipedia Commons

Additionally, at Cocos Island National Park off the coast of Costa Rica and the Galapagos Marine Reserve off the coast of Ecuador, shark tracking has revealed that scalloped hammerhead and blacktip sharks frequently habituate areas outside the current MPA boundaries. Taken together with these findings, the successes of the Malpelo Fuana and Flora Sanctuary and Revillagigedo National Park at reducing fishing suggest that extending the boundaries of these MPAs would greatly improve protection for sharks in these regions.

Blacktip shark (Carcharhinus limbatus), one of the sharks tagged in this study that lingered around particular islands. Image Source: Wikipedia Creative Commons by Amada44
Amada44, CC BY 3.0, via Wikimedia Commons
Fish are Friends and Food

By conserving sharks, we are also conserving other wildlife. Sharks are an important predator in the ocean. By hunting, they keep their prey from becoming too prevalent, protecting fisheries by maintaining balance and stability in the marine food web. For example, tiger sharks keep sea cow populations in check, which helps to protect sea grass from over-grazing. This sea grass is important habitat and food for smaller organisms and helps hold sediment in place.

Additionally, because marine protected areas can increase the catch for commercial fishers outside their borders, this conservation strategy stands to benefit both wildlife and humanity. With over 3 billion people depending on fish for their nutrition, fisheries conservation strategies like marine protected areas are essential for the future of marine life and society together.

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Julia Bebout

Julia Bebout

I am a PhD student at the University of California San Diego studying how the timing of germination and flowering shapes plant communities. I'm fascinated by how past environments can affect present and future ecosystems, especially faced with climate change. My favorite things to write about are community ecology, wetland and alpine ecosystems, and regenerative agriculture. I also love hiking, climbing, baking, and dancing! Twitter: @BeboutJulia

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